a) Field of the Invention
The invention is directed to a subassembly for generating an optically active slit with a changeable slit width s, preferably for slit lamps, with two slit plates or slit jaws which are displaceable relative to one another at a straight-line guide and between which the slit is formed, wherein one of two guide paths is allocated to each slit jaw.
b) Description of the Related Art
In optical instrument engineering, it is frequently necessary to generate illuminated fields of different geometric shapes with a virtually uniform illumination. One shape of illuminated field that is very frequently required is a light slit which is adjustable in width and length with an exactly parallel limiting of the slit width. Precision guidance of the slit-shaping structural component parts and a high edge quality at the slit jaws are needed to generate a light gap of this kind with high-contrast, sharp image borders.
A preferred application for subassemblies for generating an optically active slit is the slit lamp, which is frequently used for ophthalmologic diagnosis. It comprises essentially a stereo microscope and a projection device, both of which are arranged so as to be movable on a carrying system and coordinated with one another. The projection device makes it possible to generate geometrically different light fields. It is coupled with the stereo microscope in such a way that the center of the illumination field plane generally coincides with the center of the observation plane.
For example, a slit width which is adjustable from "zero" to 14 mm in a continuous and sensitive manner is required for applications of the kind mentioned above, wherein "zero" signifies an absolutely tight closing of the slit. The length of the slit can be between 0.3 mm and 14 mm, for example; further, the slit must often be swivelable by at least .+-.90.degree. about the optical axis.
A significant problem in slit-forming optical subassemblies continues to be that the function-related caused proximity of the light housing which contains the illumination source giving off heat causes temperature fluctuations which disadvantageously affect the parallelism of the slit and which require a slit jaw guide that still generates a light slit satisfying requirements with respect to quality in spite of the influence of temperature.
The slit jaw guides known from the prior art have straight guide elements based on sliding friction or rolling friction in which two slit jaws which are displaceable relative to one another for changing the slit width are pretensioned against a guide path arranged at the frame by means of correspondingly constructed sliding or rolling guide elements so as to be free of play.
A disadvantage in all of the known technical solutions in this respect is the transmission of thermal and mechanical influences to the slit jaws which still occurs to an undesirably high degree and the consequent unwanted influence on the slit parallelism which manifests itself, for example, in the inability of the slit to close absolutely tight. To this extent, in spite of the large number of solutions that are already known, there is still a need for development, the aim of which is to reduce the troublesome influences and their consequences.